The use of apparatus of this type has already been recommended, in particular for the protection of low-tension electric power, measurement or transmission lines against the electromagnetic effects of nuclear explosions. However, they can only protect electric lines against pulses whose voltage increases at a speed of not more than 1 kV/nanosecond. Now, it will be easily understood that powerful nuclear explosions can induce disturbances which cause the tension in a line to increase at a speed of about ten or more kilovolts per nanosecond. The limiter units or dischargers of such apparatus may fail to trigger when they are subjected to disturbances which cause an increase in tension in such a short time, or they may trigger at very high tension and therefore under circumstances where they no longer fulfill their protective function.
Preferred embodiments of the present invention produce apparatus which efficiently protects low-tension lines against disturbances of the kind which cause the tension in a line to increase by between one and several tens of kilovolts per nanosecond, corresponding to an energy of several hundreds of kilojoules and permanent power of a hundred or so Kw, at very close time intervals. Said apparatus has a high shunt impedance and leaves residual disturbances of only a few hundreds of volts.